Spinneret capillary metering plugs

ABSTRACT

A spinneret for the extrusion of fiber-forming material into shaped filaments is formed from a plate that has its upper and lower surfaces connected by a passage having successive cylindrical and capillary lengths. An insert is fitted in the cylindrical length of the passage to serve as a metering orifice with a resistance to flow at least twice that of the capillary.

United States Patent Hawkins Jan. 7, 1975 SPINNERET CAPILLARY METERINGPLUGS Inventor: Curtis Owen Hawkins, Cove City,

E. I. du Pont de Nemours and Company, Wilmington, Del.

Filed: May 10, 1973 Appl. No.: 358,858

Assignee:

US. Cl. 425/461, 425/464 Int. Cl D0ld 3/00 Field of Search 425/198,382.2, 463, 464,

References Cited UNITED STATES PATENTS 3,081,519 3/1963 Blades et a1,425/464 3,249,669 5/1966 Jamieson 264/177 F Primary Examiner-Robert D.Baldwin 3 Claims, 3 Drawing Figures l I i 11/ I PAIENTEnJm H9753,859,031

FIGJ

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(PRIOR ART) SPINNERET CAPILLARY METERING PLUGS BACKGROUND OF THEINVENTION This invention relates to extrusion of fiber formingcompositions into filamentary form, and more particularly to animprovement in multifilament spinneret assemblies leading to increasedfilament uniformity.

The improvement of filament uniformity in filaments extruded frommultiple orifice spinnerets has been and continues to be a goal ofsynthetic fiber producers. Generally, the observable nonuniformities areone or the other of two types: end-to-end or along-the-endnonuniformity. End-to-end nonuniformity refers to denier differencesbetween two filaments spun in a group of multifilaments intended to beidentical. Along-theend nonuniformity refers to variations in denieralong a single filament. Difficulty in controlling nonuniformitiesgenerally increases with the complexity in crosssectional shape ofspinning capillaries both because more complex shapes must ordinarily belarger and be cause capillary-to-capillary precision in forming isnecessarily less.

In U.S. Pat. No. 3,095,607, J. S. Cobb, Jr., disclosed an improvedspinneret assembly which sharply improves end-to-end uniformity duringmultifilament extrusion. It comprises a metering plate directly adjacentthe upstream face of the spinneret plate. The metering plate has aplurality of substantially identical circular apertures, each one inalignment with one of the like plurality of orifices in the spinneretplate. Each aperture provides at least twice the resistance to fluidflow as does its aligned orifice in the spinneret plate.

SUMMARY OF THE INVENTION The present invention is an improvement overthe above-mentioned spinneret assembly. It retains all of the advantagesof improved end-to-end uniformity while additionally providingcapability for improved along-the-end uniformity. Moreover, it reducesthe volume of fiber forming composition at its hottest state betweenfiltering and final extrusion, with the result that high temperaturedegradation and its consequent problems are diminished.

According to this invention, there is provided a spinneret for formingfibers from a polymeric material comprising: a plate having upper andlower surfaces connected by a passage, said passage having successivecylindrical, tapered and capillary lengths, and an insert fitted in saidpassage, said insert having a central axis bore in alignment with saidcapillary length, there being a concentric restriction in said bore,said restriction being sized to provide a resistance to flow of thefiber former polymeric material which is greater than the resistance toflow of the fiber forming material to the capillary length.

Tapered passage-transitions to the restriction in the bore of the insertmay be provided.

Preferably, the outside diameter of the insert over most of its lengthis enough small than the cylindrical length of the spinneret passage toprovide a sliding fit while that portion immediately adjacent the uppersurface of the spinneret is enlarged so as to require a forced fit inthe passage. Still more preferably, the upper portion of the bore of theinsert is threaded so that a threaded tool may be used for removing theinsert from the passage.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a cross section of a typicalspinneret assembly according to this invention.

FIG. 2 is an enlarged cross section of the assembly of FIG. 1 restrictedto the immediate vicinity of one extrusion orifice.

FIG. 3, similarly to FIG. 2, shows for comparison the pertinent portionof a prior art spinneret assembly as disclosed in U.S. Pat. No.3,095,607.

DESCRIPTION OF THE ILLUSTRATED EMBODIMENT Referring to the drawing,spinneret plate 10 is adapted to be mounted in a filter pack assembly 12similar to the one disclosed in U.S. Pat. No. 3,095,607. The spinneretplate 10 is provided with a plurality of passages connecting its upperand lower surfaces with each passage including a cylindrical length 14and a tapered length 16 continuing to capillary length 18. Inserts 20are fitted into these passages. Each insert includes its own axial bore22 with a concentric restriction 24 therein. Restriction 24 is sized toprovide at least twice as much flow resistance as does capillary 18 tothe flow of fiber forming polymeric material.

It is seen that cylindrical insert 20 actually has a portion 26 oflarger outside diameter which provides a forced fit in counterbore orcylindrical length 14 of the spinneret passage. The remainder of insert20 is slightly undersized to allow for a sliding fit in the passage.Preferred, but optional, passage transistions 21, 23, and 25 areemployed within the bore of insert 20. In a further preferred version,bore 22 is preferably threaded inside from its top partially down itslength so that a tool can be threaded into insert 20 for removal of theinsert from the passage of the spinneret.

FIG. 3 is a cross-section through the flow axis of an orifice similar tothat disclosed in U.S. Pat. No. 3,095,607. It has the same spinneretpassage, i.e., cylindrical,tapered and capillary lengths; but nometering plug is employed. Instead, there is provided a metering plate 3clamped to spinneret plate 1. Centered above each orifice 2 in meteringplate 3 is a metering orifice 17. Thus, it can be seen that orifice 17of FIG. 3 is equivalent to restriction 24 of FIG. 2 if both are the samesize and all else is constant. The main difference in structure beingthe different in volume between the metering orifice l7 and thecapillary in FIG. 3 and the restriction 24 and the capillary in FIG. 2.

It is believed that pulsations in the fiber forming material upstream ofthe capillary are responsible chiefly for along the end variations andthat the severity and frequency of pulsation increase with increasingvolume of fiber forming material between metering orifice and extrusioncapillary. Metering insert 20 of this invention minimizes the volume inquestion.

A second advantage of the present invention is the reduction of thermaldegradation by reducing the time during which the fiber forming materialis held up at its hottest state. The reduction in time is due toreduction in volume assuming constant flow rate. For the assembly ofthis invention (FIG. 2), the volume in question is the volume ofcylindrical length 14 less the volume occupied by metering insert 20.For the prior art assembly (FIG. 3), the corresponding volume includesnot only all of the volume ofits counterbore 14' but additionally thewhole volume of metering orifice 17 (including transition 23 andcounterbore 22').

A still further advantage is that the spinneret plate of FIG. 2 may becleaned, inventoried, and reused with metering inserts still installed.With the prior art assembly of FIG. 3, spinneret plates and meteringplates must be cleaned and inventoried separately. The additional plate3 moreover, increases the chances of leakage in assembled packs.

Fiber forming materials suitables for extrusion through the assembly ofthis invention include synthetic polymer melts and hot synthetic polymersolutions. Specific materials include, but are in no way restricted to,polyamides such as polyhexamethylene adipamide, polyesters such aspolyethylene terephthalate, polyacrylics such as polyacrylonitrile andthe like.

I claim:

1. A spinneret for melt spinning fibers from a polymeric materialcomprising: a plate having upper and lower surfaces connected by apassage, said passage have successive cylindrical, tapered and capillarylengths, and an insert fitted in said passage, said insert having acentral axial bore in alignment with said capillary length, there beinga concentric restriction in one end of said bore, said one end beingadjacent said tapered length, said restriction being sized to provide aresistance to flow of the fiber forming polymeric material which isgreater than the resistance to flow of the fiber forming material by thecapillary length.

2. The spinneret of claim 1, said restriction being sized with respectto said capillary length to provide a resistance to flow at least twiceas large the resistance to flow by the capillary length.

3. The spinneret of claim 1, said central bore in said insert beingprovided with tapered lengths before and after said restriction to formtapered transitions from the bore to the restriction.

1. A spinneret for melt spinning fibers from a polymeric materialcomprising: a plate having upper and lower surfaces connected by apassage, said passage have successive cylindrical, tapered and capillarylengths, and an insert fitted in said passage, said insert having acentral axial bore in alignment with said capillary length, there beinga concentric restriction in one end of said bore, said one end beingadjacent said tapered length, said restriction being sized to provide aresistance to flow of the fiber forming polymeric material which isgreater than the resistance to flow of the fiber forming material by thecapillary length.
 2. The spinneret of claim 1, said restriction beingsized with respect to said capillary length to provide a resistance toflow at least twice as large the resistance to flow by the capillarylength.
 3. The spinneret of claim 1, said central bore in said insertbeing provided with tapered lengths before and after said restriction toform tapered transitions from the bore to the restriction.